This invention relates to electromechanical assemblies in which heat is conducted between two components, such as an integrated circuit module and a temperature regulating unit, which are pressed together.
In the prior art, various electromechanical assemblies have been disclosed which maintain an integrated circuit chip at a certain temperature while the chip is operating. For a general background of such assemblies, see U.S. Pat. No. 4,791,983 by E. Nicol and G. Adrian entitled "Self-Aligned Liquid Cooling Assembly", and U.S. Pat. No. 4,879,629 by J. Tustaniwskyj and K. Halkola entitled "Liquid Cooled Multi-Chip Integrated Circuit Module Incorporating a Seamless Compliant Member for Leakproof Operation".
In such assemblies, heat flows between an integrated circuit chip and a temperature regulating unit along a thermal conduction path which includes one or more joints. In the case where the components of each joint are rigidly fused together, then the task of taking the joint apart in order to remove a chip is made difficult. On the other hand, in the case where a joint consists of two components that are merely pressed together, then the thermal resistance through the joint is increased.
To reduce the thermal resistance through a pressed joint, thermal greases and metal pastes have been developed. When a layer of these materials is placed in the joint, microscopic air gaps between the joined components are reduced which in turn reduces thermal resistance through the joint. Such greases and pastes are described in U.S. Pat. No. 5,056,706 by T. Dolbar, C. McKay, and R. Nelson which is entitled "Liquid Metal Paste for Thermal and Electrical Connections".
However, one drawback of a thermal grease is that its thermal conductivity is still relatively low, in comparison to the conductivity of a metal. See U.S. Pat. No. 5,056,706 at column 2, lines 24-29.
Also, another problem with the thermal grease and the metal paste is that they stick to both of the components which are pressed together in the joint. Thus, when those components are subsequently separated in order to remove a chip from the assembly, a residue portion of the grease or paste from the joint stays on both of the separated components.
If the electromechanical assembly is used to test hundreds or thousands of integrated circuit chips which are subsequently put into an end product, any grease or paste which is retained by a chip presents a problem. Specifically, the task of cleaning the residue grease/paste from each chip before the chip is put into an end product adds to the time and cost of producing the end product.
Also in the prior art, a novel pressed joint is disclosed in U.S. Pat. No. 5,323,294 by W. Layton, et al. entitled "Liquid Metal Heat Conducting Member and Integrated Circuit Package Incorporating Same." In this patent, two components are pressed together with a thin compliant body lying between them which has microscopic voids like a sponge, and a liquid metal alloy is absorbed by the compliant body and partially fills the voids.
However, one drawback of this joint is that it requires the compliant body as a carrier for the liquid metal, and this compliant body is an extra component which adds to the cost of the joint. Also, if the joint is taken apart, a portion of the liquid metal can adhere to the components that were pressing against the compliant body, and that is a residue which must be cleaned up. Further, the liquid metal in patent '294 will chemically attack aluminum and copper, and those metals often are in the electromechanical assembly. See U.S. Pat. No. 5,658,831 by W. Layton, et al, at column 7, lines 8-42. Thus, extreme care must be used to insure that no residue liquid metal is inadvertently squeezed out of the compliant body and put in contact with any aluminum or copper.
Accordingly, a primary object of the present invention is to provide an electromechanical assembly which has a thermal conduction path with a novel pressed joint that overcomes the above drawbacks of the prior art.